Customs Notice 20-39
Effective January 1, 2021, importers of qualifying goods may cite the United Kingdom Trade Continuity Remission Order, 2021 #20-1135, in order to benefit from the remission of duties. 
Importers are responsible for obtaining documentation in support of a claim for remission under the Order. The Canada Border Services Agency (CBSA) will accept documentation from exporters in the UK in support of an importer’s claim for remission.
For more information, click here.
Source: Canada Border Services Agency (CBSA)
