You may be interested in this previous answer of mine which provides answers province by province about why the Canadians did not join the Thirteen Colonies. This is actually quite a popular question in this sub and there are some shorter answers in the FAQ. You may also want to do further reading here which has links to various answers compiled by /u/Master_Gunner, as well as here where u/idrymalogist provides further information.

Briefly, all the Canadian provinces except Quebec had pretty tiny populations, often only seasonal or else non-permanent, and mostly recently resettled. They had more to lose and less to gain from a revolt than did the Thirteen Colonies. Quebec had more reason to revolt, but the threat of revolution was successfully neutralized there by the British through the Quebec Act enacted by Parliament in 1774.

That said, there were Québécois and Nova Scotians who did fight on both sides of the war. The American Patriots made an early bid to capture Nova Scotia, but lost, and upon the loss, the fervent Patriots in that colony were forced to leave. This ended any serious Patriot threat in that colony. In Quebec, the Patriots raised two regiments that fought on the side of the Americans.

Both provinces also raised troops for the British side. About 500 men enlisted in the Royal Nova Scotia Regiment, and in Quebec, there was the Quebec City Militia as well as the Quebec (provincial) Militia who fought on the side of the British. I can't find exact numbers at the moment for either militia, but it was in the hundreds if not quite a thousand troops as well.

In both cases, these Loyalists regiments spent the war years protecting their local homeland. The Royal Nova Scotians spent most of the war in Halifax, offering support services to the British Royal Navy that used the city's ports as a base for attack along the Atlantic seaboard, especially before the capture of New York City. These same men were many of the same men that had successfully defended the colony from capture by the Americans during the Battle of Fort Cumberland.

It was largely the same in Quebec. The militia troops there defended the province from the Americans at the Battle of Quebec in 1775, and spent the remainder of the war stationed in Quebec and Montreal to defend against possible future attacks.

The other provinces didn't really have enough of a population to warrant any large scale attacks or engagements, though there were some raids. For further information, see my previous response linked at the top of this post. I neglected to mention, however, New Brunswick in that post. That's because New Brunswick was still legally part of Nova Scotia until 1784, so the exile of the Patriots after the Battle of Fort Cumberland included an exile from both Nova Scotia and New Brunswick. The two modern-day provinces' histories during the war were tied up together, though there was a brief pro-Patriot rebellion leading up to the Battle of Fort Cumberland there.

I had a post related to this, which also addressed Quebec's unique situation in the Revolution:

https://www.reddit.com/r/AskHistorians/comments/dlbqkb/before_the_american_revolution_were_the_british/fcxpzf8/ u/enygma9753

This Maritime region had been known as Acadia, until the Seven Years War and the fall of New France. The British deported the Acadian population, allowing settlement by English Protestants. Some came from Britain, but many came from New England. Nova Scotia was similar to the 13 Colonies and Halifax was a major North American station for the Royal Navy. But the region was still sparsely settled in comparison to New England. It had its own legislstive assembly, which had voted in favour of loyalty to the Crown.

The average settlers at the start of the Revolution were largely indifferent to the revolution, while a small minority held secret (and illegal) pro-Patriot meetings and agitated for rebellion in 1776. This culminated in a failed attack on Fort Cumberland, which held out until reinforcements arrived from Halifax to crush the rebellion. Patriot homes and farms were razed in retaliation and sympathizers were driven out of the region, ensuring the territorial integrity of the colony for the remainder of the war.

As American privateering raids soon impacted virtually every coastal town and village during the war, the attacks turned any lingering indifference or sympathies for the Patriot cause in the Maritimes into opposition and hostility. Even George Washington held a dim view of the prospects for rebellion in Nova Scotia.

After the Revolution, some 80,000 Loyalists left the United States (many having been persecuted for their allegiance to the Crown and deprived of their property and livelihood during the Revolution). About half of these were to settle in the Canadas, with most moving to the Maritimes, including the newly-created colony of New Brunswick. They received land grants, supplies and compensation for war losses, in thanks for their service to the Crown. While some Loyalists would later return to America, those who remained would have a tremendous impact on the formation of a uniquely "Canadian" identity -- separate from that of France, Britain or America.

The Loyalist migration to Canada would have a lasting legacy on North America less than a century later, when a new nation, the Dominion of Canada, was created out of the British North America colonies in 1867.

Source:

Sprague, D.N. American Revolution - Invasion of Canada. Article. thecanadianencyclopedia.ca. 2006.

and,

Wilson, Bruce G. Loyalists in Canada. Article. thecanadianencyclopedia.ca. 2009.