Your only land connection with China right now is Nathu La Pass, a treacherous Himalayan pass which remain close six months every year during winter. Other six months are also not good for transporting goods with this winding two lane road. Look at yourself.
View attachment 679346
Image: Nathu La pass
This road is only siutable to do trade with Tibet, not China proper. Your most convenient road to China goes along Kolkata-Dhaka-Sylhet-Mandalay-Kunming corridor.
View attachment 679349
Now if you want to avoid Bangladesh to connect with ASEAN and China overland, your only option left is Siliguri Corridor, which is not adequate to connect even with your North-East, forget about ASEAN and China. Any meaningful connection with ASEAN and China requires India to keep Bangladesh on board, while Bangladesh can avoid India seamlessly with Chittagong-Cox's Bazar road/Railway going to Myanmar and China.
@bluesky