Practicalities
1) Flag
New Flag would have, say, four or five new BLUE STARS added, on the TOP of the present 51 white stars, to welcome our new states.
2) Political folding-in
Ten years before much happens politically, allowing time for current Canadian office-holders terms to more or less expire. Even thereafter, only the names on the doors would change, as a practical matter. Canadian political Houses would remain, like our State houses. Might even have to elect some Governors for some of the various new States. Current border guards would fold into our FBI/Homeland Security.
3) Currency
All Canadian currencies would enter on par with US dollars. That would probably give every Canadian pocketbook a one-time boost. I bet land values would skyrocket, too.
4) Capital punishment
Each State would decide for itself, just like the current States in the USA.