Motivation might give Milan an extra boost, but I would still be more cautious about betting on a Milan win. Lecce shouldn't be underestimated, and based on their previous match, they managed to draw against Genoa away from home. Genoa had always beaten Lecce in their last 5 encounters. Meanwhile, Milan recently played at home but were defeated by a newly promoted serie A team. So in my opinion, betting on a Milan win is a bit more risky, and I would prefer to bet on BTTS (Yes)
Lecce certainly didn't perform too badly in their first match of the season against Genoa. The draw meant Genoa and Lecce only managed to pick up one point. Based on that match, it certainly shows that Lecce shouldn't be underestimated, as they possess a strong team, which is why they earned one point, unlike Milan, who didn't even get one. However, Milan certainly needs to be wary because Lecce is a strong team, and for some people betting on the Milan-Lecce match, it will certainly be confusing to choose which team to favor.
If you're unsure about which team to favor, choosing BTTS is certainly the right choice. Many people use this technique when they're having trouble predicting. I wish you all luck in your betting. But personally, I think I'll bet on Milan to win.