"I" would consult directly with the US and Canadian Customs/Border Patrol. Good luck!I have a 3 year planned bear hunt in New Brunswick. I would like to take my Thompson Contender in 35 Remington to hunt with. It has a 14” barrel. Will that be a problem?
Short answer, yes it is a problem, you'll need a rifle or shotgun with a barrel that's a bit longer than 18".
You can't hunt with restricted or prohibited firearms in Canada. Some handguns are prohibited, and any that aren't prohibited are restricted. That alone eliminates the possibility of hunting with any handgun in Canada.
Restricted firearms also include long guns with an OAL less than ~26" or a barrel less than ~18.5". I don't remember the metric measurements off the top of my head, but an 18" barrel is too short.
The last time I checked the regs had a minimum rifle bbl length for a "modified" rifle to be 18". If a rifle was in its original configuration, the barrel could be shorter. Presumably a 16" barreled Marlin Trapper would be legal.
Bringing a handgun into Canada will most assuredly get you arrested.
A group of bear hunters shared a camp with my group in the northern most tip of Maine one year. One of the guys from the other group never made it to the camp. He took some shortcut that took him briefly in and out of Canada. He was bowhunting but brought a handgun for backup. He was arrested on the spot and held by Canadian authorities. The poor guy sat in jail until his parents got to Canada and made arrangements for him to be bailed out. The gun was forfeited and authorities said he would likely be banned from entering Canada for life. He still had to clear the criminal charges against him. It was an innocent mistake, but one that cost him dearly.
Just looked it up, it's only semis that are restricted if the barrel is less than 470mm/18.5". Modified long guns with barrels under 18" are prohibited.