To brief you on your gear choice, from the D90 days to now you'd be glad to hear that things have progressed quite a lot to the point where you can't really buy a bad current generation camera. They are basically all good.
So it's a case of picking a model that suits your needs.
As cathlights points out, you could buy the best you can afford or the minimum you can get away with. In one scenario you have room to grow, the other you have limitations that tests your creativity and forces you get the best out of your gear. In any case, once you've acquired your gear I highly recommend your biggest investment is on yourself rather than more gear. This may be purely time spent practicing or paid workshops etc.
Back to gear:
FF vs APS-C. The debate has been done to death so I'm sure you're aware of the usual arguments like low light and DOF. To give you a slightly different perspective, in terms of the associated lens there are not a lot of native choices from both Canon and Nikon. The APS-C market is much better served by third parties like Sigma or Tamron. Natively you can opt for FF lenses on APS-C cameras but then you're not using the entire image circle so you're carrying additional bulk and weight, if that matters to you. Of course you could argue that you're shooting with the best middle portion of the lens but you have to decide whether that's worth the extra bulk penalty. This largely applies from wide to short-tele lenses. Once you get to super tele focal lengths then there's little size/bulk difference.
Buying FF lenses also allows a path from APS-C to FF but buying APS-C only lenses limits their usability (if you can mount them at all) if you move to FF down the line.
If you decide on APS-C, you may want to look at APS-C only formats like the Fuji X system since there's no ambiguity about lens for what sensor size and all their lens cater only to their format.
If you decide on FF, Canon does have a largest available lens line up for FF.
I may be speaking out of my depth here with Canon gear but I believe 7D II is more geared towards high speed shooting and better suited for subjects like sports, wildlife etc. The cropped sensor is 20MP so even though the absolute pixel count is lower than the 5D III, for subject where you can't physically get closer to fill your frame, the 7D will be more advantageous because the pixel density is far higher. Ie. wildlife or sports where you're limited to how close you can get.
For general photography where you can change your shooting distance to fill your frame then there's little difference between the MP counts of all three camera.
But I stress that all three cameras are very capable and you won't really be left wanting unless there are specific genres you want to shoot with special needs. Then perhaps one model might have an edge.
