By default, when a a piece modeled in Fusion360 is prepared for 3d printing, you will notice that something designed upright like the piece below:
will up it being on its side when you bring it into most slicers, like below.
Though this is probably a minor Fusion360 annoyance, there is actually a setting to remedy this once and for all – by making the z axis the vertical axis for both Fusion360 and your slicer.
This preference can be fixed via the preferences menu, by changing “Default modeling orientation” from Y up to Z up.
While this would not retro-actively fix the modelling orientation of your previous projects, it should right things for all your new designs on-going.