The new captive has been set up to reduce claims volatility for small and medium self-funded employers, or fully insured employers transitioning to self-funding.
Legend Re will be available for 1 January 2018 policy effective dates.
According to Sun Life research, four out of 10 fully-insured employers would consider switching to self-funding and, of those, 70 percent would consider using a captive solution when switching.
It also revealed eight out of 10 brokers expect at least one of their clients to utilise a captive in the future.
Brad Nieland, vice president of stop-loss for Sun Life Financial US, commented: "Captives allow employers to pool together to share a portion of their self-funded risk, reducing claims volatility and making them a viable option for small and medium employers looking to self-fund their medical benefits."
"The partnership will draw on Pareto Captive's expertise in the client education, formation and ongoing management of group stop-loss captives, and the strength of Sun Life's stop-loss product and services."
Andrew Cavenagh, managing director of Pareto Captive, added: "Working with Sun Life as our stop-loss fronting carrier partner on this new programme brings added value to both organisations' services."
"Captives make self-funding more accessible for small and medium employers, so it is important to offer a strong stop-loss option that will give those employers the risk protection they need once they've chosen to self-fund."