If I had them both and was going to have messy sloppy fish LOL, I would run the canister AND the sump, each separately on their own lines. I don't think the intake motor on the canister would be strong enough to also power the sumps needs. What else do you have? You mentioned an overflow, which one and whats it rated at? And the canister, which make and model if you know? I'd kinda like to see what youre working with as far as equipment. And what return pump do you have? Gph?
Sorry for soo many questions but it's kinda necessary to make a decent determination. I'm hoping one of our sump experts will chime in, I'm soo not more than adequate with sumps and wet drys....I only have the one running on my 125g right now, in fact I have a lot of questions still on my upcoming 90g wet/dry setup for my newest tank. hehe...