Bitcoins don't have IDs - it's only amounts being transferred between addresses. If I have 5BTC in my wallet, I have no way to differentiate between let's say the 0.01 "canadian" and the 4.99 ordinary BTC. i could not specify which ones to send in a transaction.
That said, if MintCoin gains momentum I'm sure there will be plenty of MC-BTC exchanges popping up.
That is wrong. Maybe the current client implementation cannot do this, but the open block chain allows one to exactly see where a coin originated (i.e. whether is is Canadian or not). Alternative implementations could then be told to specifically spend the Canadian or regular coins.