This is an aspect of some people's pronunciation of English that has long puzzled me, a Scotsman. They'll say cinemar - ie put a final r where there isn't one - but pronounce star as staa - where there is!
However, I can see no point whatsoever in getting annoyed about it, given that anger at language usage has never achieved any improvement. Live with it!
Gonna - which is represented by 'gunner' in your example, Pat - has been in use as a colloquialism on both sides of the Atlantic for a century now. I guess, therefore, that it's here to stay in everyday speech, so - whilst you may not like it - you'll need to get used to it!