There is no difference between the Champix Summary of Product Characteristics (SPC) and the ones for generic varenicline. The SPCs are where you can find all the information on usage, side effects, and drug interactions of varenicline - and they are essential reading.
Link to SPC for Champix Initiation Pack: Champix Initiation Pack
Link to SPC for Champix 1mg Maintenance Pack: Champix 1mg Maintenance Pack
Link to SPC for Champix 0.5mg Maintenance Pack: Champix 0.5mg Maintenance Pack
The full Summary of Product Characteristics (SPC) for the Brown & Burk and Wave Pharma versions of varenicline are below.