Saw an ad on priceline.com for a sale at Air Canada for prices starting at $394 rt from US cities to LHR. When I try to book on AC.com, I am getting prices of $197 rt ++ comes out to about $500 with tax. This is in US pricing, $209 cad was the starting price, about $550 cad all in. ITA says $215 cad each way plus tax for these dates. I was checking DTW DCA ORD in November, there is other availability before and after that as well at varying prices.

By the way, the fares are in N class, in fact it is the only fare offered under the "economy- lowest price" tab, it says it earns 100% status miles on the fare page but, this is obviously a gray area. I would book it if I knew I would earn miles. I did not post as a mileage run deal for this reason as well, its not that great a deal in my opinion without the miles.