Usually. (Systems periodically undergo planned maintenance activities, during which time only one QPU is active through Leap.)
You can see the QPUs that are available to you in the list of solvers on the Leap Dashboard:
If you do not explicitly specify a solver when you submit a problem, the system schedules your problem on the least-busy QPU so that you receive results as soon as possible.
Choose a QPU by the properties you need. Through the Ocean tools, you can specify the type of solver you need as a dictionary of (feature, value) pairs and the software will return one that satisfies your requirements. To explicitly select a lower-noise solver, for example, specify the lower-noise attribute; this is contained within the tags property: