I've never been to Apex, so my advice is probably biased, but I can assure you as an intermediate skier you'll have a blast at Sun Peaks. Most of the trail development over the last 10 years, including Mt Morrisey which opened last year, has been focused on intermediate terrain. You can even get a taste for "tree skiing" on the groomed, gladed runs (there's enough room between the trees to groom, and make it less likely you'll hit them
. Snowboarders seem to love the mountain too.
Sun Peaks has a great little village at the base of the mountain (I hear Whistler in 1984 or Aspen in the 60's), super friendly people, I was so impressed when I visited last year that after spending the last two seasons at Whistler/Blackcomb I bought a place here.
A friend that visited Sun Peaks with me last year went to Apex with his family over Thanksgiving. He said it was also a very nice mountain, mostly north facing so not as much sun (but good for the snow). Still, he said in terms of services, accomidations, and variety of terrain he felt Sun Peaks has more to offer.
Access back to the States is very easy, multi-lane highway (Canada 5 then Canada 1) all the way to Sumas.