TORONTO (Reuters) - Some global hedge fund investors are going into 2021 optimistic about a speedy snap-back from the economic challenges related to the coronavirus pandemic. Hedge funds, which use leverage and employ more aggressive, often riskier strategies than other investors, believe many previously undesirable sectors, ranging from energy to retail, will rebound in 2021. Accounting for roughly $3 trillion in assets, hedge funds showed resilience in 2020, with many outperforming the market, according to investors.