Rachelle, the COT 320 is a fine paper -- it is what I am using for my platinum/palladium prints. But I do get better results pre-treating the paper in a bath of 5% oxalic acid...which seems to indicate it does have a slightly alkaline sizing in it. This wetting and drying the print might also help with countering some of the sizing...just a guess. You might try soaking the paper in hot water for a few minutes, then drying it before your next printing session. Just another odd-ball thing to try. Of course if you had some Oxalic acid sitting around the house, you might try soaking it in that instead of plain water. Another strange thing you could try would be to pre-coat the paper with a dilute solution (2%) of citric acid (vitamin C from the local health food store) using the rod...let it dry, then coat with your cyanotype chemicals. I have no idea what would happen...but acidity does seem to help.
Perhaps your local chemist (do you call your pharmasists that in Canada?) has a little dichromate. All you need is about 5 grams in a liter or two of water.