Your landlord has the legal right to know who they are renting their space to (i.e., YOU), but they have no right to know who your guests are so long as those guests do not cause problems (damage, noise, break the law, etc.).
Firther, they cannot discriminate against you because of your marital status or family status, so whether you have a girlfriend or not is none of their business:
http://www.ohrc.on.ca/en/human-rights-tenants-brochureYour landlord also cannot charge you more rent if your girlfriend visits, or even is she moves in –
this Toronto Star article provides some accurate information (from a former Landlord and Tenant Board adjudicator, and ACTO (tenants’ rights) lawyer).
Your landlord also cannot stop you from having guests:
https://stepstojustice.ca/questions/housing-law/can-my-landlord-stop-me-having-guestsFurther, for regular rentals (not social housing) there is nothing specified in the law anywhere that limits how long a guest may visit you.
You, and also your girlfriend, also cannot be compelled to sign a new lease if she moves in, but doesn’t sublet.
This NOW magazine article provides clarity on this from another ATCO lawyer.
Also, note the quote from Geordie Dent of the FMTA (a terrific Toronto-area tenant-rights advocate):
Some residents may find themselves living with short-term roommates who don’t plan on adding themselves to the lease. Even then, there isn’t always a requirement to provide your landlord with information about those occupants, according to Geordie Dent, FMTA’s executive director.
“As long as you’re not violating overcrowding bylaws, you’re legally allowed to have as many people as you want in your apartment,” Dent says.
But if you decide to sublet some or all of your place to your girlfriend, then you must get permission from the landlord (and the landlord is allowed to do their “due diligence” in terms of seeing the new tenant’s ID and running a credit check). In this case, your girlfriend can be used to sign a lease.
http://www.acto.ca/~actoca/assets/files/docs/TipSheet_Assignment%26Subletting_0107.pdfhttps://www.cbc.ca/news/canada/london/questions-renters-landlords-1.4751954So, so long as your girlfriend is only visiting or living there and not subletting (i.e., YOU are responsible for paying the rent, not her), then she does not have to provide her name or ID to the landlord.