It depends, of course, on their particular interests.
BC is an amazing place , both in the summer and winter
But outside the large cities there can be a bit of small town attitude
Nothing hostile, just not always that sophisticated, unless you head for the ski resorts . However, Nelson and Vancouver Island are worth seeking out.
Even if they do not intend crossing into the US it maybe useful to get an ESTA to enable them to fly around via a US airport. You need one even if you never intend to enter the US itself, but want to connect a flight, say in Portland, to save money. I'd also recommend anyone travelling to South America to get one too. It's amazing how many less expensive flights go through US airports. It's a useful tool in case plans have to change at short notice.
Montreal Vancouver and Quebec will feel more familiar
If it's a big trip, Newfoundland can be spectacular, if a little unsophisticated
Take mozzi spray or thermal knickers
Or both