Hi Zulcap
May be you can try and make the EX3200 as 2 member VC and enable no split detection, so that atleast one member stays UP in case of any issue. This will eliminate the need for RTG.
Yes J-Series router supports LACP. Refer page 6 of https://kb.juniper.net/library/CUSTOMERSERVICE/technotes/3500133-EN.pdf
Thanks
Arul