My gut feeling is that if it isn't based on Taxman/Saxman's engines, it's most likely emulation done by M2. It's definitely possible to add widescreen to Mega Drive games on a mass scale as shown by Genesis Plus GX Wide which was introduced earlier this year: With some per game patching to eliminate bugs and to compensate for the extra view distance, you can definitely pull off widescreen. Although there definitely would be some limitations dependent on the game. I'm sure M2 would be more than capable of pulling off a similar effect across many of the Mega Drive games (unsure about Sega CD or 32x, if that's even on the table for this collection). I'm not sure if the Sonic 2/3 special stages would work well for this method, unless they selectively forced 4:3 under certain scenarios. Obviously having Taxman work on it would yield a much better result (especially for the extra content on the table), but this is definitely a realistic option Sega could do.