You're better served searching on AvCanada or PilotCareerCentre for actual jobs. Also, word of mouth was huge back in the day for instructing jobs, so even if a school doesn't have a need, maybe they know of a school that does.
Is flight instructing your career goal or is it a stepping stone to something else?
I'm too far removed from the flight instructor world to honestly give you advice in the current employment outlook sphere if the answer is the former. Plus, I didn't get my instructing start in Canada, and had moved back home when that stage of my career was nearing its end. But I do remember it was difficult for a Class 4 instructor to find work outside of the school they completed their rating with. I seem to remember it primarily came down to a supervision issue - schools already had Class 4 instructors, and didn't have the space or desire to supervise another instructor, but they'd be happy to hire a Class 3 or higher. That may have changed in the last 15 to 20 years though, but the business model hasn't changed, so I would be surprised if it had. If you're serious about continuing down the instructor road, have you considered looking outside of Ontario (assuming you haven't of course)? There are a lot of busy flight schools out east and west who might be in a better position to hire a Class 4 Instructor.
If the answer to my original question is the later, that is that instructing is a stepping stone, then perhaps with 600 hours and a Group 1 Instrument Rating it is time to start looking at the 703 and 704 operators. There are a lot of open positions for First Officers on Navajos, King Airs, Beech 1900Ds, and the like around the country if you're willing to move. You'd need only write your IATRA, if it's not already written, and start throwing out the resumes. That too will require a search beyond the borders of Ontario, but rare is the pilot in Canada who hasn't had to move across the country at least once before ending up in their ideal career position. Jazz, Encore, and I believe Porter are all hiring sub-1000 hour pilots, and when it comes to the airlines, seniority (not PIC) is king. Finish out a 2 year bond on something like a King Air, and you'll have around 1,200 to 2,000 hours when applying to the airlines, which is much more attractive to the airline than 750 hours. Plus, with the PIC you've gained from instructing, you might find you're able to hold an ATPL right at 1,500 hours, putting you in line for an earlier upgrade should the opportunity arise. If the airlines is not your thing, then this option at least opens doors to other places in the industry.
Finally, and I preface this by saying that I don't want this to come off as being rude. It's not my intent at all. Rather, it is an attempt to get you to look at what you might be sending out with objective eyes. But I don't want to sugar coat it either, as that does you no good: 600 hours total time with likely 400 hours as an instructor is still low-time. Sure, it's not brand new with the ink still drying, but you'd have somewhere close to half or just over half the required instructing experience required to apply for your Class 3. I say this because it is important when applying for a job that you appear confident and collected without appearing blustery or conceited. It is an extremely fine line to walk, and I have interviewed a few pilots in my time who lost out on a job because their resume, cover letter, or comments during an interview was full of vain, boastful, or ego-building statements. Heck, I've done it myself too, once losing out on a job for going a tad overboard during the interview. The company was gracious enough to be quite honest with me, saying had it not been for that, I'd likely have been hired. I'm not saying that is what you are or are not doing, but your last sentence gave me enough of a moment of pause to suggest that you review your cover letter, resume, or general approach for any statement that could appear egotistical from the person who is receiving your documents.
Best of luck