My first recommendation will be based mostly on how you will be handling the camera, and what are your long term goals with it.
If your goal is to take better photos for yourself, and you're not inclined at becoming a professional, then a superzoom will definitely be a good choice. If you go the DSLR road, chances are you'll need at least 6 months of practice before you notice a huge improvement in your photos. That's if you take photos very regularly. If you take your camera out once a month, it'll be years before you can adjust the settings on your camera fast enough from shot to shot, and instinctively have an idea of what works in which situation.
The other recommendation will be budget-wise. The cheapest lens in the 300mm range is probably Canon's 75-300mm III which still sells for about 200$ new. It is complete rubbish, and a superzoom's lens will probably outperform this any day. The next step up is Canon's 55-250mm at 300$, which has IS and a decent image quality. Tamron's SP 70-300mm DI VC USD goes for about 500$, and is the first lens I would say is a clear improvement over a superzoom lens in that range. The next best up is Canon's 70-300 IS L USM in the 1500$ range, then you have the 300mm primes which can get expensive very quickly.
Then you have to add a camera body, which even if you go with an outdated model, will still cost you at least 200-300$ for an old model usually with an 18-55mm kit lens.
So basically the very least you could get away with is 500$ for an old DSLR with a 55-250mm, and the recommended would be at least 700$ for a 200$ DSLR and a Tamron SP 70-300mm. In both cases, you will have an old DSLR with a tiny LCD screen in the back.
But if you want to spend the time to learn how to use a DSLR, then those combos will definitely be worth it on the long run. The first day you get your DSLR, though, you'll probably feel a bit lost and probably your photos will be a bit worse than your z990's. But they will improve over time.
Cameras: Canon EOS 6D, Canon EOS Rebel T3i, Canon EOS Rebel T2i, Canon S90
Lenses: Tamron: SP 24-70mm F/2.8 Di VC USD, SP 70-300mm F/4-5.6 Di VC USD, Rokinon: 8mm Fisheye cine, Canon: EF-S 18-55mm f/3.5-5.6 IS Lens, 75-300mm f/4.0-5.6 III, and EF 50mm f/1.8 II
Retired camera: Fujifilm Finepix s700