Two points to bring up,
First, Canon's market research must come from somewhere, it's not like they invest huge amounts into product development randomly! They may consult with specialist groups of professionals for their expensive, premium pro range gear, but with their consumer level and currently absent mid-range series, it would likely be some other way. Whether they look at competitor's sales, or sales of their previous EF, EF-S and EF-M lines is a possibility, but that's a 'chicken and egg' problem if there aren't pre-existing products. They must have spoken to someone, conducted some kind of survey or research to figure that there was a market for relatively cheap, super-tele wildlife lenses before they controversially released the RF 600mm and 800mm lenses with f/11. They obviously didn't consult their pro market segment who use expensive primes and high-end zooms on that one. I have no definitive answers here, but it's something to think about.
Second, as someone familiar with running websites, I'd say that half the traffic or more on many sites comes from mobile devices. We can't assume that marketing researchers are all using desktops, and can therefore be tracked via their IP addresses. If they're using mobile devices, they may be connecting via 1. local company wifi 2. home or other remote wifi services or 3. mobile data. Only the former would use a corporate IP address if it wasn't going through a VPN. Many marketing types may be on the road often, or work from home part time. Just a few more possibilities... I'm not commenting on the likelihood that Canon scans online forums, just on the slip in reasoning.
Also worth considering, while forums may not be representative of the whole market, they probably accurately represent a specific demographic, a subsection of the non-professional enthusiast market (who also like sharing their opinions and views online), so forums are probably not without value. It wouldn't be too hard to profile the users on this forum and DPR and others, to figure which part of the market they represent, what type of gear they buy and how often, whether they are early adopters and tech buffs, how much they generally spend, and whether they would likely unquestionably swallow up whatever Canon throws out on the market. Then again, that last point may be the reason why Canon might never need to read forums, they just might be able to get a rough idea of what might sell based off some other data, and chance it because this demographic will buy everything from low to high end released for the hybrid digital camera range..