I don't have experience with that gun but any red dot that can be mounted on the rail will work. The Tasco red dot from Canadian Tire I believe should fit. Just take off the carry handle and you should be able to mount it on the rail system on the top.
Also as others have said, you should probably swap the spring it has right now for the replacement spring that comes with it (I believe it's an M100 or M110). Otherwise there's probably a pretty good chance that the gears will be stripped to shit because it's such a tough spring.
For 203 mounting, you'll need to get a rail system for the front end. As well it's tough to get a 203 into Canada so don't order from outside the country or there's a high chance that you'll get a letter from the CBSA notifying you of a seizure of your package. Get AV'ed and there will be a few floating around but to the best of my knowledge they're not that common (however there are some floating around).
ಠ_ಠLess QQ more Pew Pew
READY TO >> RACE