I will be in Chengdu from 29th April to 08 May 2017. During this time I'd like to go to Jiuzhaigou but heard it might be quite crowded due to the Labour Day. Do you reckon it is better to go on Tuesday 2nd March or it will be busy anyway and should be totally avoided ? Same question about the Buddha at Leshan :-)
Going to Jiuzhaigou during a major holiday is pretty much pointless - you can google the images of massive crowds. Avoid holidays and avoid weekends. So try to move your date as far away from may 1st as possible, so May 4th would probably be a better choice.