This study presents a scenario-based environmental and economic assessment of hybrid propulsion systems and alternative marine fuels within Panama Canal-centred maritime operations. Dual-fuel (DF) engines configured in diesel-electric and mechanical propulsion systems, as well as fuel cell/battery electrification, were evaluated across two bulk carrier case studies. Cold ironing (CI) was assessed independently to quantify its contribution to port-side emission reductions. Ammonia DF systems achieved the highest tank-to-wake (TtW) greenhouse gas (GHG) reductions, up to 78.49% with CI, while green ammonia reduced well-to-wake (WtW) emissions by 66.03%. Liquefied Natural Gas (LNG) systems achieved GHG reductions aligned with 2030 targets. Methanol offered moderate benefits, while first- and second-generation biodiesel failed to meet GHG targets and showed limited environmental viability. Economically, grey ammonia yielded the lowest levelized cost of energy ($140.61/MWh), while green ammonia reached $469.01/MWh, indicating a trade-off between sustainability and cost. LNG and methanol remained competitive under both low- and average-price scenarios. The Panama Canal's strategic location makes it a key connection hub for low-energy-density alternative fuels, which require larger storage volumes and pose trade-offs between cargo capacity and refuelling frequency. As a mid-route chokepoint, the Canal enables reliable refuelling, supporting the operational viability of zero-carbon fuels in long-haul shipping.