The Western Basin fish and Eastern Basin fish do not really mix a whole lot from what I understand. They each have their own migration patterns and neither group really crosses the Clear Creek Ridge between Long Point and Erie PA in any great numbers (I'm sure there is the odd exception to this rule though). The Western Basin Fish are still heading East and from what I gather, they are just showing up around Port Glasgow & Port Bruce. As WTP points out the US spawning Eastern Basin fish tend to migrate Eastward along the US side after spawning and then turn back West along the Canadian side towards Port Maitland. They are just starting to show around Nanticoke but not in great numbers just yet. The migration pattern of the Grand River school is not really clear yet. There are also resident fish all over the lake who just hang out and don't join the parade for whatever reason.
There is a very large study underway of the migration patterns in both the Western & Eastern Basins but there aren't a whole lot of results or conclusions yet. It is kind of interesting how they are following the fish migration though. They have radio transmitters on a large number of fish and have set up a series of radio receiver 'gates' across the lakes which record how many fish cross and where.
Here are links to the GLATOS home page, a video of the study methods, the Western basin study , & Eastern basin study pages:
http://data.glos.us/glatos/explore
http://data.glos.us/glatos/projects/13
http://data.glos.us/glatos/projects/32