The whole argument of OP seems to be revolving around one statements:
"There are a lot of non genuine people married who have PR, why will mine be a red flag?"
What you need to understand is just because some people managed to sneak through the system, it does entitle everyone else.
Second, you do not really seem to have sufficient data to prove that there are "just so many" fake couples out there having PR.
Third, no matter how genuine your relationship is, your circumstances are completely stacked against you:
i. WHV coming to an end.
ii. Marriage after just 3 months old relationship. On an average people take much more time to decide which car to buy. And we are talking a life commitment here.
iii. Your gf (sponsor) has no financial stability of her own at the moment.
To someone looking from outside the prism of emotions and human feelings, it would appear a clear cut case of someone desperately trying to extend their stay in Canada.
Also, you say you have no intentions to live in Canada as well, but you want to live with your GF forever.
This implies that at some point, she will have to leave Canada to be with you. If that is the case, why bother about PR at all?
Just like everyone else has already suggested, it is better to wait now and build a strong case in your favor. Even if it means you leaving Canada, and staying away from her for a year or so. It is still better than risking it and getting banned, right.
Or else, if you two cannot even imagine being apart for a second, then your gf may have to sacrifice her possible Canadian citizenship, and opt to live with you in your country.
The bottom line is that it's a risk you are talking about, and if it does not work out in your favor, the argument that there are so many fake couples with PR is really not gonna be of any help.