In the case of Calgary... all immigration is good for the economy it seems, there hasn't been a shortage of jobs here really, things are a bit tougher now but for a long time Calgary has been boom, boom, boom. Oh and I'm sure I'm a drain on their economy in a way... lets be honest I'm being paid to be a radio astronomer and I bet there were similarly qualified Canadians but we live in a free global market - no protectionism etc - they just go for the person who seems the best.
Oh and in the UK - immigration has been necessary, given certain English folk seem happy to sit on their arse getting their benefits not caring a speck about the world around them.