Welcome to the community!
I'm not sure I quite understand your question. I do not believe Fido carries OnePlus devices so you wouldn't be able to upgrade to that device through them. You can view the phones Fido offers here.
However, you are certainly welcome to purchase one of those phones for use on the Fido networks, providing it is unlocked. If this is the case, you should note that there are different versions of that particular phone model -- all with slightly differing network specifications.
Taken from here.
All of those models appear to have all of the compatible bands/frequencies for 2G and '3G'.
With regards to LTE, the North American model would have all of the compatible bands/frequencies. On the other hand, both the European/Asia and Chinese models would only have one compatible band/frequency, band 7 or 2600MHz. You can verify the compatible bands/frequencies here.
While all of the versions should work on the LTE network, coverage depends on matching bands/frequencies on your surrounding cellular towers. Not all bands/frequencies are available from all cellular towers. You can verify the location and bands/frequencies of your surrounding towers here.
Hope this helps