I am already in Canada with my spouse, both on open work permit. I only did it so i can get ITA earlier and as i am working full-time and work permit is about to expire. Is this not a reasonable explanation? Where do i have to provide this explanation? In EE profile after getting ITA or in OINP application?You could. But is coming on your own what you're looking for? You would also have to be able to provide a pretty reasonable and convincing explanation as to why you're going down that path, otherwise, you might find your application being rejected.
Moreover, if you do manage to get a PR approved in such a manner then you'd only be left with the option to then sponsor your spouse which can be a lengthy and painful process.
So yes, you can.... but should you?