Why stop there, what about something to recognize the southern border? "From sea to sea to sea to America?"
That only defines the country in two dimensional space, though, so after that we'll go to the volumetric motto, and finally the spacetime motto. After that it'll be something weird relating to string theory or quantum mechanics.
$1:
All three territorial premiers in 2006 pushed for the change, arguing that a three-seas motto would more fully acknowledge Nunavut, Northwest Territories and Yukon as equal partners in Confederation.
Um, the territories have coastlines along the "sea" - if anyone should feel left out, it's the provinces that don't have coastlines at any sea, like Saskatchewan.