You can fly from Manchester to Calgary with Canadian Affair, Air Transat or FlyZoom. I think you could then get an internal flight to Edmonton or drive. We flew to Calgary with Canadian Affair in June 2005 and spent a fortnight touring the Rockies - Banff, Lake Louise, Jasper and Canmore via the Icefield Parkway. The scenery is absolutely spectacular. I think it would be rather snowy in March.

Edmonton is an easy 3 hour drive from the calgary international airport, or a quick 45 minute flight. If you want to fly book with Westjet, they are the best Canadian shorthaul carrier with great prices and outstanding service.
Now, while your in Alberta, you are very close to the rockies but I would imagine your friends will take you to Jasper and Banff, don't miss it if you are here.
Also, check out westjetvacations . com, For about $300.00 canadian (130 pounds) you can get return flight and 2 nights hotel in Victoria, BC or Vancouver. The flights are about 2 hours from Edmonton, and you can go to Vancouver, then ride the Ferry over to Victoria. Also, if you go to victoria, Tofino is something to see, about a 3 hour drive from victoria.

Weather....late March early april in Calgary would be spring like (some Snow, melting, -5 to +15 degrees celcius), Edmonton would be slightly cooler, springlike but snow and melting. Jasper would be winter, as would Banff and the columbia icefields (they are between jasper and banff). Temps would be -7 to +10 degrees celcius, snow on the ground, and great skiing.

Enjoy your holiday,
Wayne