You'd have to check with the Canadian equivalent of the U.S. state Highway Patrol or DMV about the legality of swapping the trim tag. Oklahoma is the only state in the U.S. that I'm aware of where swapping or altering a trim tag is illegal.
That said, the most popular reproductions of trim tags that I know of come from
http://trimtags.com and they cost about $225 the last I read and $12 for the rivets. Don't know if they make Canadian tags or not but you could ask.
Problems are (1) you don't know all the correct information to have stamped like body date and body number and there's no way to get that information verified that I know of and (2) a reproduction trim tag is fairly easy to spot. Since you have GM of Canada docs on the car that shouldn't be too much of a problem for any future potential buyers but I'd disclose the trim tag is a reproduction (back to original colors and options) but date and body number may not be correct. If the current trim tag looks original to the car, I'd be worried about the VIN plate - maybe a Malibu SS VIN plate was swapped to your car.