New Vegas pretty much makes Van Buren non-canon in the sense that whatever Obsidian didn't use in New Vegas is not canon. If I recall correctly the only location the two games share is the Hoover Dam. There are other things it uses, of course, such as Caesar's Legion, but whatever was in Van Buren that doesn't show up in New Vegas can be ruled as non-canon from now on. Think about it this way, if developers from Black Isle didn't use something from it in their newest Fallout game, they aren't going to use it in the future, so there's no reason to consider it as canon anymore.
Well, not entirely. They might regard some of the concepts from Van Buren as canon and intend them to e.g. show up in future games, but they did not include them in New Vegas not because they're not canon or contrary to canon, but because they e.g. are too far from Vegas to appear, like Denver. And most of Van Buren, while not confirmed, will probably not be contradicted by New Vegas either, so it can be used as flavor info.
And the same applies to Fallout Tactics too - only the things mentioned in Fallout 3 are 100% confirmed as canon, and the rest of the events from Tactics could be either canon or non-canon, until confirmed either way.