Best place, bar none:
St. John's Newfoundland.
Drive a half hour south to the famous O'Brien's Charters. Whale watching and bird watching - pretty amazing. Earlier in the season you might see some icebergs too.
If you then go north from St. John's, to Trinity - drive north again to Bonavista. I have fond memories of picnicking at a coastal park in Bonavista -and watching a pod of whales (humpbacks) frolic just off the coast - for hours - when you see them, you can't tear yourself away from them.
I saw more whales there than in Nova Scotia, B.C., Alaska, combined.