Huawei P20 compatible with Fizz?

If you P20 is for the Canadian market yes, however, you need to check with the version

do you have the version?

EML-L09

EML-L29

EML-AL00

EML-TL00

For an LTE-compatible phone configured with LTE network preferences:

• 
  Calls: Your device must support HSPA 850 MHz or 1900 MHz frequencies
• 
  Mobile data: Your device must have dual-frequency support for 1700/2100 MHz (also called AWS or band IV)

Your phone can also support other frequencies that allow it to take advantage of the LTE network.

For a phone that only allows 3G or HSPA preferred:

• 
  Calls and / or mobile data: The phone must support the 1700/2100 MHz frequency (also called AWS)

Source: https://fizz.ca/en/faq/compatible-devices