@wiye if you JUST need a Canadian phone number, you can get a VoIP service like Fongo or TextNow you can pick a Canadian number when you setup
If you need a Canadian number with PM service so you can buy roaming addon, you need a new PM sim card too activate, you can activate in US but you need the sim card with you. You can buy online from Amazon and have them ship to you in US ( do not buy online from PM, it takes them long to deliver)
@wiye So you don't have an account with PM currently or your PM account is not active? If the latter, then as already mentioned, you'll need to first re-activate your plan before being able to purchase any roaming add-ons which are only available for a 10 day duration.
If you don't have an account with PM, then you need to purchase a PM SIM and activate the account before being able to do anything else. Here's a link to activate a new account if needed: https://activate.publicmobile.ca/
Can you get someone to send you the sim? Or do they mail to the states from here? Or CCS? I'm not certain about this step: then activate it but don't insert the sim yet. Set your phone to turn off automatic networks. Then wander up to the border and insert the sim and connect to the Public network. Not a US network.
Then you can buy the add-ons and connect to T-Mobile and use the Public services you bought while you're in the states.
Be aware that things are changing rapidly in the states as far as talk goes in relation to here. Text and data will be fine.
After a little research I see you have limited options for your dilemma. If only a Canadian number is required for calling and text then a voip provider is your best bet. Both fongo and textnow have been reliably used by members here. Textnow has free calling and texting....but a lot of ads. Fongo has way fewer ads but charges for outgoing texts ($4/month I believe) both offer Canadian phone numbers and enhanced services for a small fee. Their apps work on wifi or mobile data and use about 0.5mb/min.
You can look into fonus with free roaming and 20gb/month for US $30. Reviews are mixed but you can choose a Canadian phone # at activation. Here's the info on fonus by PlanHub ....
As far as Canadian providers go you are very limited unless you have an outrageously expensive postpaid plan w/roaming or pay on average $12 to $14 a day to "roam like home" on a post paid service on top of your plan amount your prepaid choices are public mobile and fizz out of Quebec. Fizz is a better deal at $35/1gb and unlimited calls/texts Canada/US roaming plan but more difficult to attain because you need a Quebec address. Either way both pm and Fizz rely on the 3G network for voice calls (Fizz for texts too!) With the decommissioning of the 3G network in the US this puts you back at square one with the need of using a voip provider for voice calls as a workaround.
As of July 1st voice services are possible using T-Mobile's 2G network where available. YMMV.