He traded with them and treated them with more respect than he showed to the barbarians who came by sea.
He allowed a small Russian trading and religious presence in Beijing, although I think they harassed it when they thought that the Russians might be harboring one of their Dzungar Mongol enemies.
Meanwhile, Qianlong pissed off the Russians by inciting a large share of the Mongols who had been settled in Russian Kalmykia, north of the Caspian, to migrate back to the Qing empire's lands.
A few Russians in the 18th century proposed campaigns to conquer some of the frontier regions ruled by Qianlong. These plans were never adopted as the Russians always had something more important to deal with in Europe or western Asia.