Real Reason I Suspect TRP Chose the SplitI think the main reason for the split is TCP believes the stigma surrounding their liquids pipelines is proving to be a drag on its share price and thus weighing down the value of the company as a whole and they likely can't get what they think they're worth via a sale of all liquids pipelines to another entity.
Ideally, it would have been best to just sell all the liquids pipeines and use the proceeds from the sale to reduce debt while keeping 100% of the Columbia Systems. They obviously want to keep their investment grade credit rating, so they needed an infusion of cash to both reduce debt and finish the money-eating Coastal Gaslink project.
As far as the Keystone XL lawsuit, good luck battling the US government. It's going to cost TRP even more money in legal fees while the US government drags it's feet, files motions to delay proceedings, and use the appeals process to the max if TRP should win an initial judgement. Perhaps TCP will eventually get a settlement sum, but it's unlikely to be anywhere close to what they're asking.