Nothing in Toppling spell states anything about attack rolls:
Toppling Spell (Metamagic)
Your spells with the force descriptor knock the affected creatures prone.
Benefit: The impact of your force spell is strong enough to knock the target prone. If the target takes damage, fails its saving throw, or is moved by your force spell, make a trip check against the target, using your caster level plus your casting ability score bonus (Wisdom for clerics, Intelligence for wizards, and so on). This does not provoke an attack of opportunity. If the check fails, the target cannot attempt to trip you or the force effect in response.
A toppling spell only affects spells with the force descriptor. A toppling spell uses up a spell slot one level higher than the spell's actual level.