France and UK combined have a far superior military with greater capability, plus nuclear options. Poland by itself is technically only in a superior defensive position, and doesn’t have the long range strike capabilities of France or UK.

That said, what would stop Polish forces from advancing are Russian military lines and deep defenses that have so far proven to be incredibly fragile behind the front lines. It’s assumed that Russia could pull in a lot more troops and equipment if needed, but reality makes that picture look a lot more shaky. Everyone thinks Russia has deep layers of defense and a million troops to move around as needed. But at the same time, their logistical failures have continued to be so immense that a coordinated attack beyond what they’re handling in Ukraine would likely strain their operations beyond usefulness.