Hmm, thats not good. It sounds like the wifi was running on your previous modem, probably with the default network names and passphrases. If you didn't have anyone using your wireless, running up your monthly bill, you were very lucky.
Have you stepped through all of the settings for your Belkin router to enable the firewall, and set up the wireless networks with their own network names (not default), passphrases (again, not default) and security settings. I'm just trying to determine here if its necessary to step you through the various pages and, set all of the items as required and ensure that your network is secure. Please don't take this as an insult as there is a very wide range of user capability and knowledge on this forum, and if anyone needs help with setting up the modem or router, I and others here are certainly willing to help out.
My guess is that stepping through all of the setttings will reveal some small detail, like the wireless data rate setting that is keeping your wireless speeds down.
Here is something to check, and that is the transmission mode for your networks, as in 802.11 b, g, n, which is on page 38 of the Belkin manual. Have a look to determine what it is set for, with n being the highest data rate available. If you need a greater range out of your router, also set it for the 20 Mhz wide channel. Whether the CGN3 is operating in Bridge mode or Gateway mode with the wifi disabled, it should not make any difference to the Belkin router.
Hmm, interesting results but something here is not making sense. Your wireless rate shouldn't be above your wired rate, not at these speeds. At close range the Belkin would probably shift to the 40 Mhz channel width giving you a higher throughput. What level of service are you presently on? It sounds like 60 Mb/s but I'd just like to be sure. I would have thought that with external antenna, the Belkin would be better than the CGN3, as the CGN3 is not known for steller wifi performance. Just read through some of the comments on the forum to see that. I would wonder if running a factory reset on the Belkin would be an idea and reset all of your parameters.
After a little hunting I found a PC Magazine review dated Mar 2009. That would put the design date for this router around 2007 with a build date around 2008, early 2009. Those dates could possibly slide back a little further. Reading through the manual it references Draft 802.11n. That standard was drafted in 2007 and approved in 2009. Unless you have updated the firmware, its possible that your router is still running under 2007 draft 802.11n specs. If there were any substantive changes from draft to final version I would wonder of the possibility of running into incompatibilities now between the Belkin and newer devices. Food for thought I think. I think the major consideration is the change in processing capabilities between 2007 and now for router processors. Like anything else, time and technology doesn't wait for anyone, and although I am loath to advise anyone to spend any more money than they have to, it might be time to consider a newer router with better processing capabilities. That will depend on what your requirements are for wired and wireless connectivity in your home.
I still can't figure out why you would see reduced performance with the Belkin, with the CGN3 running in Bridge mode, as compared to your older modem, as the only link between the two is an ethernet link. Looking back at the datasheets for previous Rogers modems, they appear to have 10/100/1000 Mb/s ports, going back to the SMC modem, so, the data rate between the Belkin and the modem should be the same, unless you were running a very old modem previously. Its definitely a head scratcher at this point. Might have to say I'm stumped