Intel updates their CPUs in a tick-tock cycle. One generation they will update the CPU architecture. Next generation they will use the same architecture but shrink it down to a smaller size. So Broadwell has the same architecture as Haswell, it's just be shrunk down from 22 nm to 14 nm.
The same will be true of Skylake and Cannonlake. They will share the same architecture, but Cannonlake will be a die shrink.
In practical terms, that means performance will be almost identical, just that Cannonlake will use less power (and generate less heat). Intel usually updates the graphics every generation, so Cannonlake's integrated GPU will probably be better than Skylake's. But you're planning to use a GTX 970 for video so that won't...