Is Canadian Champagne really Champagne?

That depends on your point of view. If you don't get upset by people offering you a Coke when it's actually Pepsi, then yes. If you do, then no.

The word "Champagne" is sort of like a brand. It means a sparkling wine, prepared in a certain way, made in a particular region of France from grapes grown in that region of France.

Wines made in the exact same way, using grapes genetically identical, but in a different location are not, technically, "Champagne." They should be called by some other name, or generically "sparkling wine". However, everyone outside of Europe except a few wine snobs largely ignores this. (In Europe, it's illegal to sell wines from outside the Champagne region as "Champagne." In the US... not so much.) So Asti Spumante, another sparkling wine from Europe, is called that rather than "Italian Champagne" (Asti Spumante is not Champagne. For one thing, it tastes much better.)