Your Canada visa needs to be valid on the day you enter Canada. Your allowed duration of stay is not related to the visa validity period. This you already found out yourself from the official source, so it's not clear why you continue to doubt it.
Normally you will be given six months. Note, though, that your passport must be valid for the entire duration of your stay in Canada. You should renew your passport if necessary before returning. If you don't, and your passport expires in less than six months, you will be given entry only until the passport expiration date.
But you can only apply for a new visitor visa inside Canada if it is a study or work visa. For other types of temporary visitor visas (e.g. business, tourist, transit) you need to apply outside Canada.
You also should be aware that you have spent a large amount of time in Canada recently, so you may find it more difficult to convince the immigration officer that you will leave Canada at the end of your next visit.