From the Canadian Encyclopedia:

A Mari usque ad Mare (“From Sea to Sea”), Canada’s motto, was derived from Psalm 72:8, which reads in Latin “Et dominabitur a mari usque ad mare, et a flumine usque ad terminos terrae,” and in the King James version, “He shall have dominion also from sea to sea, and from the river unto the ends of the earth.” Attention was first directed to the verse when, apparently at the suggestion of Samuel Leonard TILLEY, the term “dominion” was chosen to represent Canada as a whole when the British North America Act was drafted.

“From sea to sea” could not apply to Canada until 1871, when BC joined Confederation and the Dominion extended from Atlantic to Pacific. In 1872 Rev George Monro GRANT crossed the country as secretary to Sandford FLEMING, who was then in charge of the Pacific railway surveys. The next year he published Ocean to Ocean, his journal describing the journey. The title is akin to “from sea to sea” and strong tradition insists that thereafter Grant preached in many centres using Psalm 72:8 as his text and advocating the adoption of “from sea to sea” as Canada’s motto.

The first official use came in 1906, when the phrase was engraved on the head of the mace of the Legislative Assembly of the new Province of Saskatchewan. This would be known to Joseph POPE, undersecretary of state at the time, and the phrase evidently impressed him. In 1919 Pope was named to a 4-member committee appointed by the federal government to recommend a new design for the Arms of Canada. No motto was included in the old design, but one was to be included in the new arms. A draft design, which included the motto, was approved by Cabinet in April 1921 and by King George V in May. Major-General W.G. Gwatkin, one of the committee members, had proposed that the motto be In memoriam in spem (“In memory, in hope”), but Pope’s counterproposal was adopted. On 29 September 1921, after viewing the final design, he wrote in his diary: “Our Arms are very handsome … everything that can be desired. The motto ‘A Mari usque ad Mare,’ which is an original suggestion of my own, I regard as very appropriate.” See also EMBLEMS OF CANADA; HERALDRY.

Psalm 72

Give the King Your Justice

Of Solomon.

1Give the king your justice, O God,

and your righteousness to the royal son!

2May he judge your people with righteousness,

and your poor with justice!

3Let the mountains bear prosperity for the people,

and the hills, in righteousness!

4May he defend the cause of the poor of the people,

give deliverance to the children of the needy,

and crush the oppressor!

5May they fear you while the sun endures,

and as long as the moon, throughout all generations!

6May he be like rain that falls on the mown grass,

like showers that water the earth!

7In his days may the righteous flourish,

and peace abound, till the moon be no more!

8May he have dominion from sea to sea,

and from the River to the ends of the earth!

9May desert tribes bow down before him,

and his enemies lick the dust!

10May the kings of Tarshish and of the coastlands

render him tribute;

may the kings of Sheba and Seba

bring gifts!

11May all kings fall down before him,

all nations serve him!

12For he delivers the needy when he calls,

the poor and him who has no helper.

13He has pity on the weak and the needy,

and saves the lives of the needy.

14From oppression and violence he redeems their life,

and precious is their blood in his sight.

15Long may he live;

may gold of Sheba be given to him!

May prayer be made for him continually,

and blessings invoked for him all the day!

16May there be abundance of grain in the land;

on the tops of the mountains may it wave;

may its fruit be like Lebanon;

and may people blossom in the cities

like the grass of the field!

17 May his name endure forever,

his fame continue as long as the sun!

May people be blessed in him,

all nations call him blessed!

18 Blessed be the LORD, the God of Israel,

who alone does wondrous things.

19Blessed be his glorious name forever;

may the whole earth be filled with his glory!

Amen and Amen!

20 The prayers of David, the son of Jesse, are ended.

From the Treasury of David:

Verse 8. He shall have dominion also from sea to sea. Wide spread shall be the rule of Messiah; only the Land’s End shall end his territory: to the Ultima Thule shall his sceptre be extended. From Pacific to Atlantic, and from Atlantic to Pacific, he shall be Lord, and the oceans which surround each pole shall be beneath his sway. All other power shall be subordinate to his; no rival nor antagonist shall he know. Men speak of the Emperor of all the Russias, but Jesus shall be Ruler of all mankind.

And from the river unto the ends of the earth. Start where you will, by any river you choose, and Messiah’s kingdom shall reach on to the utmost bounds of the round world. As Solomon’s realm embraced all the land of promise, and left no unconquered margin; so shall the Son of David rule all lands given him in the better covenant, and leave no nation to pine beneath the tyranny of the prince of darkness. We are encouraged by such a passage as this to look for the Saviour’s universal reign; whether before or after his personal advent we leave for the discussion of others. In this Psalm, at least, we see a personal monarch, and he is the central figure, the focus of all the glory; not his servant, but himself do we see possessing the dominion and dispensing the government. Personal pronouns referring to our great King are constantly occurring in this Psalm; he has dominion kings fall down before him, and serve him; for he delivers, he spares, he saves, he lives, and daily is he praised.

May the motto of this country be truly realized in revival from Newfoundland to British Columbia; from Atlantic to Pacific to Arctic, for the praise of our glorious God, the salvation of the inhabitants of the country and the good of His people, the church.