Assuming you're talking about the WHD Weir/Harvie Passage by Pierce Estate park, you can't really go around it now since it's under construction. Or at least you might want to check it the night before since water levels and other obstructions are changing on the daily.
I also believe you have to portage around that area anyways as they have a barrier going across the river before the weir to keep kayakers and canoers out until it can be made safe again. A lot of folks have perished or nearly perished in that short stretch of water. It used to be called the drowning machine:
http://www.theglobeandmail.com/news/...rticle4277142/
You can actually see the barriers here 51.044761, -114.018886 on google maps in sat view.
I would say get out just after the bridge where you can see the rafts stacked up, portage around and put back in at the 17th Ave SE bridge or thereabouts.
Good luck and be careful!