Thanks for all the great ideas ladies (and sorry for the late reply, had a very busy weekend). I ended up blotting gently with warm water, and then washing gently with warm water and a little Oxy Clean. Once the water dried, the slime that was left on the sole solidified and I was able to peel it right off; there is still some slime shine on the canvas, but it's no longer sticky at least. I'm going to try a light salt spray tonight and hopefully that'll melt off the rest of it.
Kim, don't worry there aren't slugs invading my house; I was outside standing on the bark, but it was nighttime so I couldn't see that there was a slug