The answer is that it's an old jsp site. So it's a long domain that's not good. So say this, say my company does appliances (they don't but let's pretend) and they own refrigerators.com and dryers.com and blenders.com. They have a bad domain structure and have been doing dryers.companyname.com/index.jsp?c_id=dry for years. This, of course, isn't as easy to link to. Also, to make things worse, they have 302'd dryers.com. So, after changing the response codes from 302 to 301, some of the SERPs started to include the vanity URL (i.e. dryers.com) but didn't include others (i.e. say blenders.com is still blenders.companyname.com/index.jsp?c_id=ble). I'd like them to have all the same SERP listing and it's ideal for them to be the vanity (wouldn't you rather dryers.com vs that long ugly URL). Also I know this is not the long term fix (someday it'll all be company.com/dryers but that day is not today).
So my question really is: I'm hesitant on putting a canonical on a site that is a vanity though and 301 redirecting but I have no evidence to back this up. Can you help me find the answer with evidence for this?