I'd known about "British North America's" oblique involvement in the American Civil War since I was very young, thanks to some comic book history of the conflict that I was given when I was about 6 or 7 years old. Some of the panels covered Confederates scheming sabotage north of the border in the loyal states. Then, some years later, I discovered that Clement Vallandigham, the notorious Copperhead, set up his base in Windsor, Ontario, across the river from where I grew up.
However, I was not aware of how substantial Canada's contribution was in terms of supplying volunteers for the conflict. Of course, Collections Canada has an online exhibit of some photographs and printed matter related to the Canadian Civil War, but these all focus on the contribution to the Union cause; undestandable, since the subject of the exhibit is the anti-slavery movement in Canada. Yet some Canadians volunteered for service in the Confederate army, too.
Not quite a hat-tip, but some ackowledgment is due to Gates of Vienna, via Small Dead Animals, who put me on the track of this topic.