Can I retain my exsting number plate and continue to drive the car while i have de-registered (myself) from the (plate issuing) canton and registered (myself) in another canton?
Or in other words, can I be resident of one canton while owning a car in another?
Unfortunately you cannot, here is one source and there are threads on here with the same answer. A large part will be due to the insurance and where the car is kept overnight since the premium will vary from address to address.
It should be done in 14 days, and you need to notify the traffic office in your new canton about the change of registered address for your licence too.
If you still own a home and parking space in the old canton you can usually also register a car or more there. It’s supposed to be registered where it lives and is mostly used.
I am not sure what the rules are in other cantons, but in Zug you can get your plate placed on a retention certificate and then you are free to auction on ricardo or other trading platform. However bear in mind that the admin costs might exceed the value you paid e.g. in Zug it costs CHF 250 to transfer from one owner to the other.
Edit: If your canton is not listed on the number trade website, my guess is its not that easy.