The Wii U has generic USB HID drivers for the Portal of Power. Regardless of whether you launch via disc or WUP, the Portal is identified by the software.
Skylanders Giants (Wii U) WUP Write-up The Wii U version of Skylanders Giants skylanders giants wii u wup
Search for the title ID or the full name "Skylanders Giants" within Wii U USB Helper’s database. The database pulls from Nintendo’s old update servers and user-dumped discs. Download the main game package (usually split into 20+ .app, .h3, and .tmd files). The Wii U has generic USB HID drivers
Amazon.com: Skylanders Giants Game Only for the WII U (Renewed) skylanders giants wii u wup