Yes, I absolutely DO believe that Canada could beat the US in a war. 🇨🇦
The last time the USA tried Canada on for size was the War of 1812 and the USA pretty much had it's own ass handed back to itself to take back home and have sewn back on.
The USA has never done very well in wars, not because of a lack of military hardware which it has plenty of, but because of a distinct lack of strategic military intelligence, meaning most things the US military puts it's hands on are not intelligent decisions.
Case in point, the last two wars the US got itself involved with in most recent history was Vietnam and Afghanistan. In both cases, the USA retreated from battle and went home empty handed after spending about 18 years in Vietnam and around the same length of time in Afghanistan. Extreme embarrassment for the USA with close to 60,000 US Service Personnel lost in that combined but totally failed effort.
Not to be outdone by the Russian military, Americans can sleep peacefully at night in knowing that the Russian Army also failed to win a war it started in Afghanistan long before the USA showed up to do the same thing and Russia too went skulking back to Moscow with hat in hand to receive a much-deserved public spanking in the town square by the Kremlin boss after they got back home.
The USA lost the war in Vietnam because American Forces proved themselves to be abysmally poor at jungle warfare, despite fighter jets and napalm used against a bunch of seasoned North Vietnamese jungle fighters who showed up for the party with spears, jungle snares and World War I-style machine guns which took two men to operate and transport around the jungle.
The USA lost the war in Afghanistan because American Forces proved themselves to be abysmally poor at mountain warfare as well, despite carpet bombing by B-52's, spy satellite technology, lots of ammunition and an endless supply of US government money to support America's insurgency into Afghanistan.
All of this from the American side was used against a bunch of seasoned Afghan rebel mountain fighters who showed up for the party with Russian made single-shot rifles and mountain goats and a little bit of mobile internet which one can purchase in America for their boat or mobile home from a Big Box store, who somehow managed to outsmart those very intelligent American Forces for almost 18 years.
For the record, the USA has LOST every single war that it started in the last 113 years and if the USA makes the fatal error of attempting to start another war with Canada, history would suggest that the USA would either retreat from battle which it usually does when things aren't going like the boss said they should, or they'll simply be handed their ass back to them in a picnic basket after being led to the border crossing and told to fukk off for the second time.