I’ve done a few implementations throughout my career. I’ll assume non profit means the lower the price tag the better. Both ADP and Ceridian will do the job. Just keep in mind the lower cost products out there (including ADP and Ceridian) you fit into their business model, very little customization. So flexibility is key.
Whether you are union or not, all software should be able to handle it. When are you planning on doing the implementation? What are you using now? Are the reports you need imported to Sage just the Payroll JE, or are you looking at other reports.