The best recent estimates are that between 33,000 and 55,000 men from British North America (BNA) served in the Union army, and a few hundred in the Confederate army. Many of them already lived in the United States and were joined by volunteers signed up in Canada by Union recruiters.[18] About 2,500 of those British North Americans were Black, with most serving in the US Army and a few hundred in the navy.[19]

Canada refused to return about 15,000 American deserters and draft dodgers.[20]

Calixa Lavallée was a French-Canadian musician and Union officer during the American Civil War who later composed the music for “O Canada”, which officially became the national anthem of Canada in 1980. In 1857, he moved to the United States and lived in Rhode Island where he enlisted in the 4th Rhode Island Volunteers of the Union army during the American Civil War, attaining the rank of lieutenant.

Canadian-born Edward P. Doherty was a Union Army officer who formed and led the detachment of Union soldiers that captured and killed John Wilkes Booth, the assassin of Lincoln, in a Virginia barn on April 26, 1865, 12 days after Lincoln was fatally shot.

Canadian-born Sarah Emma Edmonds was a noted Union spy.

One of the longest-living Canadians to have fought in the American Civil War was James Beach Moore, who died on August 29, 1931.

Anderson Ruffin Abbott was a Toronto-born son of free people of color who had fled Alabama after their store was ransacked. Canada’s first Black physician, he applied for a commission as an assistant surgeon in the Union Army in February 1863, but his offer was evidently not accepted. That April, he applied to be a “medical cadet” in the United States Colored Troops, but was finally accepted as a civilian surgeon under contract. He served in Washington, D.C., from June 1863 to August 1865, first at the Contraband Hospital which became Freedmen’s Hospital. He then went to a hospital in Arlington, Virginia. Receiving numerous commendations and becoming popular in Washington society, Abbott was one of only 13 black surgeons to serve in the Civil War, a fact that fostered a friendly relationship between him and the president.[21] On the night of Lincoln’s assassination, Abbott accompanied Elizabeth Keckley to the Petersen House and returned to his lodgings that evening. After Lincoln’s death, Mary Todd Lincoln presented Abbott with the plaid shawl that Lincoln had worn to his 1861 inauguration.[22][23]

At least 29 Canadian-born men were awarded the Medal of Honor.[24]