They're same except 하루하루 can't be used as an adverb. For example, you can say "매일매일이 행복하길 바라. or 하루하루가 행복하길 바라." when you want to say "I wish everyday is a happy day for you." to your Korean friend. Also, you can say "I study Korean everyday. 난 매일매일 한국어를 공부해." to them, but you can't say "난 하루하루 한국어를 공부해." 하루하루 is lighter/cuter than 매일매일. 매일매일 is 每日每日 in Chinese character. Hope this helps.

매일매일 means every single day. So we usually use that word when we describe doing something regularly.For example, I do excercize 매일매일(everyday). 하루하루 means almost same meaning but nuiance is little bit different. Usually it's little bit negative. For example,let say 'Everyday is same!!!' Then you can use 하루하루가 똑같아. 하루하루 is same. but you can use 매일매일 instead of 하루하루 cuz 매일매일 is kinda neutral expression. But 하루하루 usually include negative meaning such as bored with or sick of sth.