Let's get this out of the way: Cat shutting down the Electro-Motive Diesel plant in London was a terrible thing, and it was clear that they were in no way willing to make any offers in good faith. They had endured much longer strikes in the past, and generally came to the table with far less of a take-it-or-leave-it mentality to their position.
That said, there was (and still is) a lot of disinformation flying around about the plant, and when criticizing the closing it helps not to speak of a tax cut that didn't really exist—at least, not in the way that the Star editorial linked to describes it.
(For those who don't want to follow that link: what occurred was a change to the tax code in 2008, two years before Cat bought EMD, that allowed owners of locomotives to depreciate them at a higher rate. This incentivizes earlier replacement of the machines, which in turn benefits the manufacturers that these replacements are then purchased from. Given that the benefits applied to all locomotives owned by Canadian firms, regardless of the country they were manufactured in, this certainly wasn't negotiated for any one particular plant.)