As the page linked above indicates, the original version of Mr. Monster is the creation of Canadian Fred Kelly. It seems the character only appeared in one book, Super Duper Comics #3 in 1947 but that adventure indeed took place in Canada. If you're interested in checking it out, you can download/preview it here.
After coming across a copy of that book in the early 70's, Michael T. Gilbert modernized the character, making his version the son of the original and adding loads of back story. That Mr. Monster only saw the light of day in Vanguard Illustrated #7 in 1984, but quickly developed a following in the mid and late 80's. The bulk of Mr. Monster's material was published during those years by Eclipse and Dark Horse and the latter included the character in its "Dark Horse Presents" book as recently as last year.
Now Ghost Woman's status is a bit more murky, but it appears to have certain similarities. Here is a page from Star Studded Comics #1 (1945) which displays the character.
This isn't solid. It is only an unsupported mention on Wikipedia's page about Ghost Woman which I have not been able to confirm to this point. Here it is:
The first publication to use the name was published in 1945 by Cambridge House Publishers, and featured Captain Combat, Comandette, Red Rogue, Ghost Woman (the inspiration for the later Dark Horse Comics character, The Ghost), and several other characters.Really now?
The Dark Horse Ghost is most certainly not Canadian, having first appeared during that company's "Comics Greatest World" launch in 1993 and being based in a city called Arcadia. Much of the storyline revolved around the main character's attempts to piece together details of her past.
After a decade or so of inactivity, Ghost is currently appearing in Dark Horse Presents, the same book in which Mr. Monster resurfaced last summer.
Both being occult-based characters, presently published by Dark Horse and with a history of cross-overs (Mr. Monster with Airboy, Ghost with The Shadow, Hellboy and even the Cassandra Cain version of Batgirl), there would appear to be very few roadblocks in making this happen. It wouldn't technically be Canadian characters meeting, mind you, but apparently two characters with little-known Canadian origins.
As a final note, Ghost Woman was brought back briefly in the unfinished Northern Guard series from Moonstone. She is second from the left in the picture below, but her role was minimal in the two issues that were published.
Lastly, I want to draw attention to something pretty damn great that Mr Gilbert is said to have done for Mr. Monster's creator Fred Kelly. How cool is that?