An outland application would be the way forward, especially as your wife is returning back here to the UK.
I believe it is possible to complete an outland application whilst inside Canada too, although i'm unsure of the technicalities of this.
An outland application is also a quicker timeline than an inland application and there is nothing to stop your wife revisiting during the application process, so long as you can provide proof that she will return to the UK after each visit until the process is completed. Search for Dual intent for more details of this.
If she is with you for a little while longer, it may be beneficial to download and start the application forms whilst you can both look through them together and begin to outline the finer details in question. This may save you some valuable time.
The application, once the sponsor's part has been processed at CPC Mississauga, will be sent to the visa office in London.
One point to note, if there will be changes to residential addresses during the application process, be sure to keep the visa offices updated of these.