In British English the answer 'What are you planning to do on the weekend?' is actually WRONG. You only use on for individual days - so you would say on Saturday or on Sunday but you would always say 'AT the weekend'.
Out of curiosity, is the question mark at the end of your last sentence Canadian? I'm the States by the way? But seriously, "on the weekend" is okay. But I'd probably say "this weekend" or "next weekend."