Great work with the drawings, and interesting idea for an AU, although with number of serious issues, that were mostly already mentioned.
On a note, I guess it's worth mentioning, that potential war with USA was a major element of Canadian war planning until around 1930s (after all, except for expeditionary operations they didn't had many other options to prepare for
) - and these plans generally involved assumption of heavy British participation (rather obviously, considering then-political/administrative relationship between Canada and GB).
@Trojan
It's definitely neither time nor place for in-depth discussions about it, but saying that
slavery was the question that created the CSA in the first place is actually an oversimplification. Core of the question was the issue of states' rights vs. powers of federal government - and while imposition of slavery was indeed one of these rights, very notorious (and therefore very convenient to use in propaganda) and very important to southern economy, but it wasn't the slavery only and in itself that caused the secession.