I have both the Pixma Pro 1 and Pro 100. I am fortunate to work in the printing industry so get to use a lot of different papers in my printers. I have never tried anything above 120 lb. cover weight, but have never had an issue running 120 lb. through either printer. 120 lb. is also equivalent to 12 point. This is fairly heavy cover stock.
I have run gloss, matte, offset, photo and art cover stocks. None have ever been an issue.
I am sure that either printer could handle heavier but have never had a request for it. The only thing I do make sure of when running heavy card stock is to have the right grain. Since you will be feeding by the short side of the stock you will require short grain stock. This will make the stock more flexible going through your printer.
You will like the Pro 1 once you get use to it. I have done some beautiful work with my Pixma printers. They just require some learning and a large footprint. Canon make a very good line of printers, as does Epson.