For an unconditional call forwarding, this is *21# to turn it on and #21# to turn it off. You have to dial **21*(destination number)# to program the number you want your calls forwarded to.
For a conditional call forwarding:
Call forward busy: *67# to turn it on, #67# to turn it off. To program the number, this is **67*(destination number)#
Call forward no reply: *61# to turn it on, #61# to turn it off. To program the number, this is **61*(destination number)#
Call forward not reachable (device turned off): *62# to turn it on, #62# to turn it off. To program the number, this is **62*(destination number)#
Tech support can't remove voicemail, nor any services for that matter. But you don't have to remove voicemail to configure conditional forwarding. This can usually be set directly inside the phone. If you give us your device brand and model, we can give you the steps to get it set up!
It is like pulling teeth to get a list of working MII codes out of Videotron. For me the codes mentioned here work as long as VoLTE is turned off on your cellular profile. Turning VoLTE on, which is increasingly needed for reliable cell service, breaks call forwarding for me on multiple unlocked phones.
The current FAQ for mobility around international calls says: "You may only forward calls to numbers in Canada or the United States.
If you forward calls to a phone number outside your local calling area, you will be billed the usual long-distance charges if calls are taken or forwarded to voice mail." Basically if you can forward your phone you can try it and it might work with surcharges.
I eventually after some hoops I found the MMI codes for forwarding do work with VoLTE turned on my profile with the Google Pixel 4A. I'm going to switch to a Google Pixel 5 for compatibility. Videotron support can check if a given VoLTE phone is compatible with their network.