Would it be worth it to spend some time in Malmo on the train trip from Copenhagen to Stockholm? I know you could do a day trip, but since the train stops there anyway I thought it might be worth it to spend a little time and do a canal trip or have lunch. Thank you!
It depends on how much time you have. I don't think you should do it if it means you don't have enough time to see everything you want to see in Copenhagen or Stockholm.
I would personally recommend Lund over Malmö. Lund is older (and smaller) than Malmö, and it's more charming IMO. There are direct regional trains Copenhagen-Malmö-Lund every 10-20 minutes, and the trains to Stockholm stop in Lund as well.
I don't mean to be nitpicking, but for questions about stops in Sweden, the Sweden forum might be a better idea.
However, I agree that if you want to stop somewhere, Lund is a far better option.
I also recommend Lund. The canal tour in Malmö is nice but you can fit Lund on the same day if you start early.