Coinsandcanada.com

I received this proof set, is this a double die I found?

You will find here a similar coin to yours.

https://www.coincommunity.com/forum/top ... double,die

The first conclusion was "Flat Field Doubling", but after quick reading of all posts, the conclusion is not clear.

The link will point out to additional reference. I didn't take time to read everything for now!

I vote for MD on this 5 year old thread, not doubled

I agree with you. I vote for Mechanical Doubling

Traditional Flat field Doubling is usually more related to Proof coin manufacturing where a double strikes techniques is used.