I think the ultimate plan is to connect Highway 404 with Highway 11, creating an alternative around Lake Simcoe and ultimately taking stress of the 400.
This (old) map from Wikipedia shows proposed 400-Series Highways. As you can see, Highway 427 would indeed curve and meet the 400.
Main article:
http://en.wikipedia.org/wiki/400-series_highways
On top of this, I'd like to see the 403 extended to meet with the 402. This would create a desperately needed freeway in north London, and would take stress off the 401 between the 402 and 403.
I agree with nfitz, some of the proposed alignments on that map are downright bizarre.
Regarding the whole Lake Simcoe issue, what I'd ideally like to see is the 404 continue up around the east side of the lake, and connect with Highway 11 (which would gradually have it's at-grade sections upgraded, even though it's nearly all twinned now), making the 404 the main highway up to North Bay (and ending at the 11/17 junction). The connection between 404 and 11 would occur north of Orillia, in order to bypass much of the harder-to-upgrade 4 lane section between Orillia and Gravenhurst. I'm thinking connect in somewhere near Severn Bridge.
And I'd like to see the 427 continue north and connect with the 400 somewhere between Highways 9 and 89. But rather than stopping at the 400, I'd like to see it actually terminate at the 404, providing a good connection between the 3 N-S highways.
And while we're on the topic of highway upgrades, I drove to North Bay from Ottawa this weekend, and it looks like the extension of the 417 (which is basically just a twinning of the existing Highway 17) is almost done between the edge of the City of Ottawa and just passed Arnprior. They're doing the decking on the 2nd bridge over the Madawaska now, and a few more overpasses need to be finished. Projected finish time based on the signs is Fall 2012, which looks pretty reasonable right now.
They also have a 2nd roadbed roughed in for a few KMs beyond the end of the current twinning, so they may be starting a 2nd phase once this phase is done. Haven't read anything about it though. There's a lot of traffic between Arnprior and Renfrew, so if any section of 17 is going to be upgraded next, it'll be that section.
