Poke around the Electronics/Audio subforum, there's some information for people who have done double-din installs. Here's some of the stuff that people have already done to fit standard double-din radios in BRZs;
Double-din adapters for stock opening:http://www.ft86club.com/forums/showthread.php?t=122274
https://www.japanparts.com/parts/detail/43320 or
https://www.amazon.com/Metra-95-8202...ca3dfbb1618f22
Canadian dash trim with standard rectangular opening: https://parts.subaru.com/p/__Limited...6077CA200.html or
https://www.mysubarustore.com/oem-pa...bly-66077ca200
Clip for center trim part
https://parts.subaru.com/p/Subaru__/...909130092.html
Diagram for the dash parts:
