Hi there,
I believe you are referring to the BEPC spin out. Similar to when BIP.UN did this with BIPC, the share dropped in relation to the value of BEPC shares. But, BEPC and BEP.UN have the same economic value (IE one share = one share), and shareholders received 1 BEPC share for every BEP.UN share held, the value of the holdings haven't changed.
Which one you hold is irrelevant in terms of value. As mentioned, one share of BEPC is worth one share of BEP.UN. The difference is in the tax treatment of the companies and the dividends. BEPC is more attractive to US consumers, and if you hold outside of a registered account it may also be attractive as the dividend will be deemed 'eligible' for tax purposes. BEP.UN distributions contain a mix of eligible and non-eligible dividends which can be confusing come tax time. if held in a TFSA or RRSP, there is no difference.
Mat