I have a lot of 8-10 lb mono line.  Is this sufficient for catching lmb in a canal?  I'm using a spinning reel. 

Yup, I've caught thousands with 8, 10 & 12 lb nylon.

8 and 10 is perfect for spinning

90% of what I use on spinning reels is 8# line the rest is 6# line. You will be fine.

In fact, the cover you're fishing usually plays a larger role in deciding line-test than the fish.

Most any bass can be landed with 10-lb nylon line, but in heavy cover you might be happier with heavier line.

 

Roger

I use mono from 6 to 20 for bass fishing. Six and eight pound test is fine for finesse spinning applications, especially away from super heavy cover. But sometimes you do have to downsize to get bit at all in tough conditions. I would say 70% of my bass fishing is with 10 to 15 pound line.

If you're needing to use anything stronger than #8 mono on a spinning reel, you would be better off using braid. It will handle far better than heavier mono.