Can I ask to only be considered for one of the programs under Express Entry?

No. Under Express Entry, the system will find which programs you qualify for based on the answers you give in your profile. If you qualify for more than one program, we will decide which one to issue the invitation to apply under.

You can choose to decline an invitation to apply if it is not under the program you were interested in. But, if you do this, there is no guarantee that you will be invited again under a different program.