I may give some ideas for your case. Bascially, you only studied 3 years for university which means euqal to advanced diploma in Canada.
I know that some countries have different education system so that you mention that it's bachelor degree.. Unfortunately, some first countries require to study at least 4 years which is equal to bachelor degree. You can study pre-master program instead. Please, searching about pre- master program. And then you can explain why you have to take some course(ex; your country dont offer 4 years course for chemistry, and u want to make sure to study 4 years for bachelor degree level by Canadian education system <- I think, it's a good reason)
Good luck!