This is a fascinating and historical set of Gold-Plated Brass Die Trials issued by the Royal Canadian Mint. Only the reverse die was used to strike the uniface die trials. Struck in brass with reeded edges, they were then gold plated and encased in lucite to present to a few Canadian and International banks and gold bullion dealers. These die trials showcased the newly issued and designed Gold Maple Leaf coin series.
The $50 (1 oz) was struck starting in 1979, the $20 (1/2 oz) in 1986, the $10 (1/4 oz) in 1982, the $5 (1/10 oz) in 1982 and the $1 (1/20 oz) in 1993. The Royal Canadian Mint also struck a few uniface die trials of the Maple Leaf series in brass, with plain edges. Below is a picture of the only known set of $20 (1/2 oz) obverse and reverse brass die trials of the Maple Leaf, certified Specimen 66 by PCGS.
It is unknown whether the brass die trials with plain edges were part of the testing done by the Royal Canadian Mint as they struck the gold plated die trials with reeded edges or whether the brass specimens were a separate trial test.