Unfortunately its not, just read it in the Explosives Regulations C.R.C., c. 599 — March 18, 2013 clause 136, and 137......
Here are the regulations.Please show me where this mythical 3/4" plywood box with brass hinges is specified:
136. In this Part, “suitable receptacle” means a substantial box or substantial container,
(a) that may be placed inside a building that is not itself adapted for the keeping of explosives;
(b) the location of which is not changed from that prescribed by an inspector or under provincial or municipal law;
(c) that is kept away from goods of an inflammable nature; and
(d)
that is of easy access for removal in case of fire.
137. In regard to any receptacle, the following provisions shall be observed:
(a) it shall be provided with a closely fitting lid secured by a lock, and hinges and fastenings,
preferably of copper or brass, and otherwise closed and secured so as to prevent unauthorized persons having access thereto, and shall be kept locked except when required to be open for receipt or removal of explosives, or other necessary purpose;
(b) it shall be exclusively used for the keeping of explosives;
(c) it shall be made of wood, copper
or other suitable material;
(d) the interior of the receptacle and all fittings therein shall be so constructed, covered or lined as to prevent the exposure of any iron or steel, or of any hard or gritty surface, or the entry, detaching, or accumulating of grit, iron, steel or similar substance;
(e) the interior of the receptacle shall be kept scrupulously clean; and
(f) the receptacle shall have the word “EXPLOSIVES” conspicuously displayed thereon on a contrasting background.
Read the bold points and think outside the box.Nothing there specifically says that something other than a wooden or copper box is "suitable" and "Preferably" is not "must or shall".
The part most people don't notice is the part where whatever you are storing the powder in has to be easy to remove in case of fire.Many guys use wooden built in cabinets which are not portable and therefore don't meet the regs.
There are numerous threads on this topic already.