I heard back from Elections Ontario regarding making my own lawn signs.
You can create and display your own lawn sign, however please note that all political advertising must name the entity/person authorizing the advertising. No specific language is required for the authorization but it must be apparent what person or entity has caused the advertisement to appear and any other person or entity that has sponsored or paid for it. An example of appropriate authorization wording is “Authorized by the XYZ entity”.
Every person or entity spending $500 or more on political advertising in either the six months before a fixed date general election (the non-election period) or during an election period and who is not a registered candidate, political party, or constituency association, must register with Elections Ontario. Registration is not required where the third party is spending less than $500 on political advertising in either the non-election period or the election period.
During the blackout period [includes the day before polling day and polling day for all elections], lawn signs displayed are not considered to be paid commercial third party political advertising and can appear at any time.
So.
This is a link to a Google Docs document with the "Anyone But Ford" sign, letter-sized.
This is for 22"x17" ("C" paper) signs, and
this is for 24"x18" ("Arch C") size. The lawn signage that consists of a plastic sheath over a sturdy wire frame is usually 24"x18". It's illegal to disturb (legal) election signage, but these signs are often used for illegal commercial advertising (AKA "street spam"), and repurposing some of those would be helping to keep your neighborhood tidy. I'm hoping to get my signs up tomorrow once I've got them printed.
There will also be the matter of setting up a camera to watch them. Might as well catch a few Ford Nation types vandalising them, while I'm at it.