I just returned from a business trip to Vancouver last week, and yes, it was raining. It rains there pretty much all winter. Maybe one week of snowfall every year. But Whistler is a different story altogether, so don't let that deter you from going. I have never skied there, but I hear that if it's raining in the village, that usually means it's snowing up on the slopes. Being coastal, there are many micro-climates in the area, and you can experience three different weather conditions in the same run some days.
As for conditions in March, it all depends on the year they are having. Last season they had phenomenal snow right through the end on March and into April. Being another La Nina year, I would check the predictions to see if they are expecting the same for March/2013.
Some travel tips:
-- definitely fly into Vancouver; it's a nice modern airport, and there are shuttles that will take you up the coast to Whistler, so you don't need a rental car (unless you want to explore on your own, but then you could rent for a day or two right in Whistler).
-- depending on where you're flying from (eastern US, I think), if you fly to Vancouver and need to make a flight connection, DO NOT take a flight that connects in Canada somewhere, as your baggage will not be checked through to Vancouver; you will have to retrieve your luggage at the connecting airport, clear Customs, recheck your luggage, then catch the next flight....a pain in the rear. Get a connection in Chicago or Denver or somewhere like that, that will take you directly from the US into Vancouver so you avoid all that. Gary can verify -- he once left his skis behind in Toronto and had to ski some poorly-tuned, too-long, too-stiff loaners from a friend until his arrived days later
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-- expect to rent powder skis, so scope out the rental shops before you go, and reserve a day or two ahead if the forecast is looking good; there are lots of really good rental shops in the village, with no shortage of high-end skis on offer.
Let us know if this pans out.
Enjoy Canadian beer, much bigger kick than the stuff we drink south of the border.
Mike -- some of the best beer I have ever tasted has been from the multitude of micro-breweries in the US. The quality and variety down there are just fantastic, and to my mind, some of them are the equal of what the centuries-old European brewers are making. The Canadian micro-brew scene is slowly catching up and finally making some good products. But we still have no equivalent to say, an Ommegang or New Belgium, for instance, and some of the IPA's and American Pale Ales I have had south of the border have been outstanding, with nothing like it to be found here. However, you are correct in that the average mainstream Canadian beer (Labatts, Molson, Moosehead...) has a fuller flavour than the American equivalent (Bud, Coors, Miller...). The latter taste like dishwater to me, but a pint of Molson or Labatts is only slightly better to my palate.