first, welcome to this community.
second, before making any real project try to read all of its documents and do some tests with it.
on canvas select scale with screen size and drag anchors to fill the place you want. so your object scales to fill in different phone screen sizes and ratios.
about particles and obstacles, it depends what tools are you using. if you use unity builtin particles, you can define colliders for you particles that is a very heavy feature. and define a box collider for your obstacles. if you use UI particles and those obstacles are UI, there is no builtin feature for it you have to search what works best for you.
please share your inspector for score text and obstacle for more complete answer.